DESCRIPTION (appended verbatim from investigator's abstract): Alone among vertebrates, urodele amphibians are able to regenerate lost body parts as adults. Our strategy is to use axolotls (Ambvstoma mexicanum! to discover the signals that trigger the regeneration response, in the belief that these signals have enormous potential and consequences for human health. Our long term goals are to identify the regeneration enabling signals in limbs, in order to support progress towards the eventual application of these molecules to the Specific Aims. In the first, we will use assays derived from the extensive experimental history of regeneration of limbs, to test the roles of several signaling molecules known to be essential for limb development. These assays will use virally driven ectopic expression to examine the signals that initiate regeneration, those that are needed to establish a blastema, as well as those that are required for intercalary growth between the new limb tip and the amputation plane. We will test the role of fibroblast growth factors in the initiation of outgrowth, the role of bone morphogenetic proteins in promoting healing and inhibiting regeneration, the role of sonic hedgehog in providing the asymmetry needed to establish the blastema, and the role on Wnt factors in intercalary growth. In the second Specific Aim, we will generate a library of cDNAs made from regenerating limbs at different stages, and screen it with forward and reverse subtracted probes to enrich it for genes expressed differentially during regeneration. The library will be arrayed for efficient use, and screened with stage specific probes to identify genes expressed at different times in regeneration; We are especially interested in any novel factors that might be involved in transforming the differentiated limb stump into a blastema. Candidate genes will be assayed as described for known signaling molecules. The tools and knowledge are in place to attack complex systems, and understanding regeneration is likely to lead to new approaches and therapies for replacing or repairing lost, damaged or diseased parts of the body.